1. Field of the Invention
The present invention relates to a computer system and external storage therefor. In particular, the computer system includes devices or nodes which have peculiar device ID's (identifiers) and are connected with one another through an interface or network, such as SCSI, IPI (Intelligent Peripheral Interface) or Ethernet, for exchanging data, commands, messages etc.
2. Related Art
As stipulated in, for example, ANSI X3. 131--1986, "Small Computer System Interface (SCSI)" issued by ANSI (American National Standards Institute), the peripheral devices of a prior-art computer system have peculiar device ID's, respectively. The LBA (Logical Block Address) lengths of the devices, the types of the devices (such as a random access device, a sequential access device, a rewritable device, and a read only device), etc. are fixed for the respective devices by standards. In addition, although not standardized, management for the data reliabilities of the individual peripheral devices, management for backing up the devices, etc. are carried out for the respective devices at the request of the OS (operating system) of a host computer.
The prior-art technique is incapable of or has difficulty coping with a case, for example, where a magnetic disk storage device having a large capacity is divided into a plurality of partitions with the intention of managing the partitions as separate storage areas having different characteristics (in points of the LBA lengths, the backup management, etc.). Accordingly, expensive and large-sized magnetic disk storage devices need to be installed for respective sorts of data of different properties, such as ordinary file data and image data.
Further, there is no consideration for sharing the peripheral devices between a plurality of hosts. The exclusive control between the hosts in the case of a shared magnetic disk storage device cannot be performed on the device side, and is inevitably entrusted to the management of the host side. For this reason, it is possible that some operations of the user of the computer system may bring about a situation where data held in the magnetic disk storage device are destroyed.
Further, in case of a network including therein a node which is physically connected in the same network, but which uses a communication protocol differing from that of the other nodes, it is difficult for such a single node to use two communication protocols properly and therefore the single node has difficulty communicating with the other nodes. Therefore, expensive and large-sized magnetic disk storage devices must be installed for the respective different communication protocols.